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From 8708b9e081192786c027bb7f5f23d76dbe5c19e8 Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Mon, 6 Feb 2023 14:51:25 -0700
Subject: [PATCH] [GPOS] Avoid O(n^2) behavior in mark-attachment
Upstream-Status: Backport from [https://github.com/harfbuzz/harfbuzz/commit/8708b9e081192786c027bb7f5f23d76dbe5c19e8]
Comment1: The Original Patch [https://github.com/harfbuzz/harfbuzz/commit/85be877925ddbf34f74a1229f3ca1716bb6170dc] causes regression and was reverted. This Patch completes the fix.
Comment2: The Patch contained files MarkBasePosFormat1.hh and MarkLigPosFormat1.hh which were moved from hb-ot-layout-gpos-table.hh as per https://github.com/harfbuzz/harfbuzz/commit/197d9a5c994eb41c8c89b7b958b26b1eacfeeb00
CVE: CVE-2023-25193
Signed-off-by: Siddharth Doshi <sdoshi@mvista.com>
---
src/hb-ot-layout-gpos-table.hh | 101 ++++++++++++++++++++++++---------
src/hb-ot-layout-gsubgpos.hh | 5 +-
2 files changed, 77 insertions(+), 29 deletions(-)
diff --git a/src/hb-ot-layout-gpos-table.hh b/src/hb-ot-layout-gpos-table.hh
index 024312d..88df13d 100644
--- a/src/hb-ot-layout-gpos-table.hh
+++ b/src/hb-ot-layout-gpos-table.hh
@@ -1458,6 +1458,25 @@ struct MarkBasePosFormat1
const Coverage &get_coverage () const { return this+markCoverage; }
+ static inline bool accept (hb_buffer_t *buffer, unsigned idx)
+ {
+ /* We only want to attach to the first of a MultipleSubst sequence.
+ * https://github.com/harfbuzz/harfbuzz/issues/740
+ * Reject others...
+ * ...but stop if we find a mark in the MultipleSubst sequence:
+ * https://github.com/harfbuzz/harfbuzz/issues/1020 */
+ return !_hb_glyph_info_multiplied (&buffer->info[idx]) ||
+ 0 == _hb_glyph_info_get_lig_comp (&buffer->info[idx]) ||
+ (idx == 0 ||
+ _hb_glyph_info_is_mark (&buffer->info[idx - 1]) ||
+ !_hb_glyph_info_multiplied (&buffer->info[idx - 1]) ||
+ _hb_glyph_info_get_lig_id (&buffer->info[idx]) !=
+ _hb_glyph_info_get_lig_id (&buffer->info[idx - 1]) ||
+ _hb_glyph_info_get_lig_comp (&buffer->info[idx]) !=
+ _hb_glyph_info_get_lig_comp (&buffer->info[idx - 1]) + 1
+ );
+ }
+
bool apply (hb_ot_apply_context_t *c) const
{
TRACE_APPLY (this);
@@ -1465,37 +1484,46 @@ struct MarkBasePosFormat1
unsigned int mark_index = (this+markCoverage).get_coverage (buffer->cur().codepoint);
if (likely (mark_index == NOT_COVERED)) return_trace (false);
- /* Now we search backwards for a non-mark glyph */
+ /* Now we search backwards for a non-mark glyph.
+ * We don't use skippy_iter.prev() to avoid O(n^2) behavior. */
+
hb_ot_apply_context_t::skipping_iterator_t &skippy_iter = c->iter_input;
- skippy_iter.reset (buffer->idx, 1);
skippy_iter.set_lookup_props (LookupFlag::IgnoreMarks);
- do {
- if (!skippy_iter.prev ()) return_trace (false);
- /* We only want to attach to the first of a MultipleSubst sequence.
- * https://github.com/harfbuzz/harfbuzz/issues/740
- * Reject others...
- * ...but stop if we find a mark in the MultipleSubst sequence:
- * https://github.com/harfbuzz/harfbuzz/issues/1020 */
- if (!_hb_glyph_info_multiplied (&buffer->info[skippy_iter.idx]) ||
- 0 == _hb_glyph_info_get_lig_comp (&buffer->info[skippy_iter.idx]) ||
- (skippy_iter.idx == 0 ||
- _hb_glyph_info_is_mark (&buffer->info[skippy_iter.idx - 1]) ||
- _hb_glyph_info_get_lig_id (&buffer->info[skippy_iter.idx]) !=
- _hb_glyph_info_get_lig_id (&buffer->info[skippy_iter.idx - 1]) ||
- _hb_glyph_info_get_lig_comp (&buffer->info[skippy_iter.idx]) !=
- _hb_glyph_info_get_lig_comp (&buffer->info[skippy_iter.idx - 1]) + 1
- ))
- break;
- skippy_iter.reject ();
- } while (true);
+ unsigned j;
+ for (j = buffer->idx; j > c->last_base_until; j--)
+ {
+ auto match = skippy_iter.match (buffer->info[j - 1]);
+ if (match == skippy_iter.MATCH)
+ {
+ if (!accept (buffer, j - 1))
+ match = skippy_iter.SKIP;
+ }
+ if (match == skippy_iter.MATCH)
+ {
+ c->last_base = (signed) j - 1;
+ break;
+ }
+ }
+ c->last_base_until = buffer->idx;
+ if (c->last_base == -1)
+ {
+ buffer->unsafe_to_concat_from_outbuffer (0, buffer->idx + 1);
+ return_trace (false);
+ }
+
+ unsigned idx = (unsigned) c->last_base;
/* Checking that matched glyph is actually a base glyph by GDEF is too strong; disabled */
- //if (!_hb_glyph_info_is_base_glyph (&buffer->info[skippy_iter.idx])) { return_trace (false); }
+ //if (!_hb_glyph_info_is_base_glyph (&buffer->info[idx])) { return_trace (false); }
- unsigned int base_index = (this+baseCoverage).get_coverage (buffer->info[skippy_iter.idx].codepoint);
+ unsigned int base_index = (this+baseCoverage).get_coverage (buffer->info[idx].codepoint);
if (base_index == NOT_COVERED) return_trace (false);
+ {
+ buffer->unsafe_to_concat_from_outbuffer (idx, buffer->idx + 1);
+ return_trace (false);
+ }
- return_trace ((this+markArray).apply (c, mark_index, base_index, this+baseArray, classCount, skippy_iter.idx));
+ return_trace ((this+markArray).apply (c, mark_index, base_index, this+baseArray, classCount, idx));
}
bool subset (hb_subset_context_t *c) const
@@ -1587,15 +1615,32 @@ struct MarkLigPosFormat1
if (likely (mark_index == NOT_COVERED)) return_trace (false);
/* Now we search backwards for a non-mark glyph */
+
hb_ot_apply_context_t::skipping_iterator_t &skippy_iter = c->iter_input;
- skippy_iter.reset (buffer->idx, 1);
skippy_iter.set_lookup_props (LookupFlag::IgnoreMarks);
- if (!skippy_iter.prev ()) return_trace (false);
+
+ unsigned j;
+ for (j = buffer->idx; j > c->last_base_until; j--)
+ {
+ auto match = skippy_iter.match (buffer->info[j - 1]);
+ if (match == skippy_iter.MATCH)
+ {
+ c->last_base = (signed) j - 1;
+ break;
+ }
+ }
+ c->last_base_until = buffer->idx;
+ if (c->last_base == -1)
+ {
+ buffer->unsafe_to_concat_from_outbuffer (0, buffer->idx + 1);
+ return_trace (false);
+ }
+
+ j = (unsigned) c->last_base;
/* Checking that matched glyph is actually a ligature by GDEF is too strong; disabled */
- //if (!_hb_glyph_info_is_ligature (&buffer->info[skippy_iter.idx])) { return_trace (false); }
+ //if (!_hb_glyph_info_is_ligature (&buffer->info[idx])) { return_trace (false); }
- unsigned int j = skippy_iter.idx;
unsigned int lig_index = (this+ligatureCoverage).get_coverage (buffer->info[j].codepoint);
if (lig_index == NOT_COVERED) return_trace (false);
diff --git a/src/hb-ot-layout-gsubgpos.hh b/src/hb-ot-layout-gsubgpos.hh
index 5a7e564..437123c 100644
--- a/src/hb-ot-layout-gsubgpos.hh
+++ b/src/hb-ot-layout-gsubgpos.hh
@@ -503,6 +503,9 @@ struct hb_ot_apply_context_t :
uint32_t random_state;
+ signed last_base = -1; // GPOS uses
+ unsigned last_base_until = 0; // GPOS uses
+
hb_ot_apply_context_t (unsigned int table_index_,
hb_font_t *font_,
hb_buffer_t *buffer_) :
@@ -536,7 +539,7 @@ struct hb_ot_apply_context_t :
iter_context.init (this, true);
}
- void set_lookup_mask (hb_mask_t mask) { lookup_mask = mask; init_iters (); }
+ void set_lookup_mask (hb_mask_t mask) { lookup_mask = mask; last_base = -1; last_base_until = 0; init_iters (); }
void set_auto_zwj (bool auto_zwj_) { auto_zwj = auto_zwj_; init_iters (); }
void set_auto_zwnj (bool auto_zwnj_) { auto_zwnj = auto_zwnj_; init_iters (); }
void set_random (bool random_) { random = random_; }
--
2.25.1
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